This invention relates to a processing solution for photographic material and its processing method, particularly to a processing solution to be used for bleaching of image silver in processing of a light-sensitive silver halide photographic material and its processing method.
Bleaching solution, bleach-fixing solution and reducer have been known as a processing solution for photographic material having bleaching ability.
Among them, this kind of processing solution in processing of a light-sensitive silver halide photographic material employes widely an inorganic oxidizing agent such as red prussiate, bichromate, etc. as the oxidizing agent for bleaching image silver.
However, some serious drawbacks have been pointed out for the processing solutions having bleaching ability containing these inorganic oxidizing agents. For example, red prussiate and bichromate are relative excellent in bleaching power of image silver, but there is a fear of generation of cyanide ions or hexavalent chromium ions harmful to human bodies, thus having undesirable properties in prevention of pollution. Also, since these oxidizing agents have very strong oxidizing power and oxidize the solubilizing agent for silver halide such as thiosulfates, they can hardly be permitted to co-exist in the same processing solution. Thus, it is almost impossible to use these oxidizing agents in a bleach-fixing bath, whereby the object of making processing quick and simple can hardly be accomplished. Further, the processing solution containing these inorganic oxidizing agents has the drawback that the waste solution can be regenerated without being discarded with difficulty.
In contrast, recently, processing solutions employing an organic metal chelate compound such as aminopolycarboxylic acid metal complex have been used widely as the processing solution which is free from the problems in pollution and can meet the requirements of speed-up and simplification of processing as well as regenerability of waste solution.
As the aminopolycarboxylic acid metal complex to be used as the oxidizing agent, iron, copper and cobalt complexes of ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyalkylethylenediamine, diethylenetriaminepentaacetic acid and the like have been known. However, the processing solutions employing these aminopolycarboxylic acid metal complexes, due to slow oxidizing power, are delayed in bleaching speed (oxidation speed) of the image silver (metal silver) formed in the developing step, and therefore are not suited for the object of quick processing. Of these processing solutions, the processing solution employing iron salt of ethylenediaminetetraacetic acid (hereinafter called EDTA iron complex) is considered to be superior to other aminopolycarboxylic acid metal complexes with respect to bleaching power, and practically applied in a part of the business, but it is still inferior in bleaching power than the red prussiate type bleaching solution which has been used in the prior art. Accordingly, efforts have been made to use a bleaching accelerator, but no satisfactory result has not yet been obtained. Also, aminopolycarboxylic acid metal complexes other than the EDTA iron complex are weak in bleaching power, and when these are to be applied for processing solutions having bleaching ability, the concentration of said aminopolycarboxylic acid metal complexes is required to made higher, which is limited in economy and solubility. Thus, it has been considered that practical application of them is almost impossible. Further, in the bleach-fixing solution employing the aminopolycarboxylic acid metal complex of the prior art, when carrying out bleach-fixing processing immediately after the step containing a reducing agent such as color developer, etc., the reducing agent will be brought about into the bleach-fixing bath, or the aminopolycarboxylic acid metal complex will be reduced by the reducing agent in the bleach-fixing solution, whereby the reduced product of the aminopolycarboxylic acid metal complex reduces the color forming dye, particularly cyan dye, to the leuco form. As a result, the dye image becomes tinted in red, or contamination or stain occurs on the processed image surface due to lowering in bleaching power of the aminopolycarboxylic acid metal complex, whereby no stisfactory color reproduction can disadvantageously be obtained.
Further, in the bleach-fixing solution employing an aminopolycarboxylic acid metal complex of the prior art, there is the drawback that the sulfite ion used as the preservative disappears by oxidation over prolonged storage, whereby thioulfate ions used as the fixing agent may be oxidized to generate sulfur or silver sulfate. Furthermore, when bleaching or bleach-fixing processing is performed immediately after the color developing processing for shortening of the processing time, the color developing solution is brought about by the light-sensitive material into the bleaching bath or bleach-fixing bath, whereby there is involved the drawback that the color developing agent is liable to be oxidized by the bleaching agent to generate tar.